1. Field of the Invention
The present invention relates to in-situ methods of producing oil shale, gas shale, geothermal areas, and gas (methane) hydrates, and more particularly but not by way of limitation, to methods of forming fractures in formations by injecting liquified gases into at least one substantially horizontally disposed fracturing borehole drilled into the formation.
2. Brief Description of Related Art
Oil shale formations underlie large sections of Western Colorado, Eastern Utah and Southern Wyoming. These formations can be several thousand feet thick and contain more than 500 billion barrels of oil shale oil. Such oil shale formations consist of rock minerals combined with kerogen, a carbonaceous material which is solid material combined with rock minerals.
Earlier attempts to produce oil shale oil largely consisted of surface mining, crushing, and retorting. The efforts proved too costly and environmentally unfriendly. However, at temperatures between six hundred and nine hundred degrees Fahrenheit, the kerogen liquefies and becomes mobile. This process is referred to as pyrolysis. In pyrolysis, kerogen is either heated with hot gases or steam, or undergoes combustion by igniting the kerogen itself and injecting air or oxygen to support combustion.
After the kerogen beyond the combustion front reaches a temperature of 600 to 900 degrees Fahrenheit, the lighter elements liquify and migrate away. What remains, is the residual and less desirable components of the kerogen and it is the residual and less desirable components that are consumed in the combustion process.
When drilling into gas hydrate zones in subterranean formations problems are often encountered because the heat of drilling fluids warms the hydrates near the wellbore, dissociating them and creating craters and sink holes against the casing wellbore.
Therefore, new and improved methods are being sought for producing oil shale oil, gas shale, geothermal areas, and gas from gas hydrates in-situ which overcome various problems, including those described above. It is to such new and improved methods that the present invention is directed.